Power-saving mode for portable communication devices

ABSTRACT

Apparatus for ensuring that, in a portable, battery-powered communication package incorporating at least two communication devices, such as a combination cellular telephone and a pager, sufficient power is provided for extended operation of the communication device having the lowest continuous power consumption requirements when the device having a higher continuous power consumption rate has consumed a selected portion of the total power initially available to the combined devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/758,838, filed Jan. 10, 2001, pending, which is a continuation ofapplication Ser. No. 09/066,616, filed Apr. 24, 1998, now U.S. Pat. No.6,201,977, issued Mar. 13, 2001.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention. This invention relates to portable,battery-powered communication devices such as cellular telephones andpagers. More particularly, it relates to a portable communication deviceincorporating both a cellular telephone and a pager. It also relates tomethods and devices for extending battery life during operation of suchdevices.

[0003] State of the Art. During the past two decades, rapidproliferation of portable communication devices has been nothing shortof amazing. During the past 15 years, cellular telephones haveprogressed from being a novelty to a ubiquitous appliance. The use ofpager devices has also become widespread.

[0004] The following equipment examples are illustrative of the currentstate of this burgeoning industry. In the latter half of 1996, Nokia, amanufacturer of communications equipment, announced the introduction ofthe Nokia 9000 Communicator, a portable communication system thatcombines digital, voice and data services, as well as personal organizerfunctions in a single, compact unit. The Nokia device incorporatesprocessing capability provided by an Intel 24 MHz 386 microprocessor,flash memory, and a powerful, memory-efficient graphical user interface(GUI) operating system named GEOS developed by Geoworks, Inc. The Nokiacommunication system is designed to work in combination with a hand-heldcomputer screen produced by Reflection Technology, Inc., a manufacturerof virtual display technology and wireless messaging equipment. Thecomputer screen, which displays a full 12-inch page of graphics andtext, connects with cellular or land phone lines to allow a mobile userto receive, read, store and send faxes without the use of a laptopcomputer. The device features a virtual keyboard with which the user maycreate memos and respond to faxes, and a full-screen menu that allowsusers to choose certain functions, such as view, send, enlarge andreduce. The device can store approximately 25 pages and has a built-indirectory that stores more than 100 names and fax numbers for use withthe unit's auto-dial feature.

[0005] In the case of a portable combination electronic device, one ofthe constituent devices typically consumes more power than the otherduring operation. A combination portable communication deviceincorporating both a cellular telephone and a pager is one suchcombination device. Power consumption of the cellular phone,particularly in the transceive mode, is typically several orders ofmagnitude greater than that of a pager device. For example, a typicalcellular telephone with a 400 mAh nickel-cadmium battery will operate inthe transmit-receive mode for only about 70 minutes before the batterymust be charged or replaced. Standby time for the same battery is about17 hours. Most of the power consumed during standby mode is required tooperate the periodic query function which maintains cellular phoneorientation with respect to the cellular grid. Pagers, on the otherhand, require far less power to operate because they are, in the mostbasic mode of operation, merely radio receivers. Thus, they aregenerally endowed with much greater battery life. A standard beeperpowered by a single AA-size alkaline power cell will operatecontinuously for four to six weeks if only the beeper notification modeis employed. Operating the same pager in the vibrator notification modecan halve battery life.

[0006] When a pager device and a cellular phone are combined into asingle unit having a single battery power supply, maximum usefuloperating life of the pager between battery charges is largely dictatedby battery life of the cellular telephone operating in standby mode.When the transmit-receive mode is employed, operating life of the pageron a single charge can be cut dramatically. This is particularly truewhere the user has little control over the number of incoming calls.Thus, even though the pager function may be more critical to the user,the pager function may be rendered useless by incoming telephone callswhich drain the battery to the point where both the pager function andthe telephone function are inoperative due to battery discharge belowthe critical operating voltage.

[0007]FIG. 1 depicts a circuit which has heretofore been utilized tocontrol one of two or more electronic devices powered by a singledepletable power supply where the device to be controlled requires aclock signal input for operation. A precision reference voltage VR issupplied to the inverting terminal (i.e., the “−” terminal) ofcomparator 102, and a sample voltage VS (taken from a voltage divider101 constructed from resistors R1 and R2) is supplied to thenon-inverting terminal (i.e., the “+” terminal) of comparator 102. Thevalues of resistors R1 and R2 are selected so that the sample voltage VSis greater than VR, with the difference between VS and VR correspondingto the voltage range selected for continuous operation of an electronicdevice. The intermediate output VO1 from comparator 102 is fed to one ofa pair of inputs to NAND gate 103. A clock signal CLK is fed to theother input. As long as VS is greater than VR, the current path throughresistor R3 will maintain VO1 high, and an inverted clock signal CLK*will be passed through NAND gate 103. When VS drops below VR, comparator102 will pull VO1 low. The signal CLK* is utilized to operate a seconddevice. In order to prevent oscillations about the set turnoff point,hysteresis is provided at the output via a feedback path 104 throughresistor R4.

BRIEF SUMMARY OF THE INVENTION

[0008] The invention includes a method and apparatus for ensuring that,in an electro-chemically powered system which incorporates at least twocommunication devices packaged in a single unit, such as a combinationcellular telephone and pager, or a combination hand-held computer andpager, sufficient power is provided for extended operation of thecommunication device having the lowest continuous power consumptionrequirements when the device having a higher continuous powerconsumption rate has consumed a selected portion of the total powerinitially available to the combined devices. In the case of theaforestated first exemplary system (i.e., a combination cellulartelephone and pager), cellular telephone function is disabled when aselected portion of the total power initially available is consumed. Asa method of a first embodiment of the invention which may be implementedwith multiple communication devices powered by a single battery in whichvoltage varies somewhat linearly as a function of charge level,operation of the high-power-consumption device is disabled when a presetbattery charge level is reached. This preset voltage level is well abovethe critical operating voltage of the pager and corresponds to a batterydischarge level that is still able to provide pager operation for anextended period. A second embodiment of the invention, in method form,involves providing a separate power supply for the low-power-consumptioncommunication device for which operation for an extended period must bemaintained. As an apparatus, in combination with a combinationcommunication device, the first embodiment of the invention may includea headroom-limited flyback power supply which powers the high-powerconsumption device. When headroom drops below a minimum set by aseries-coupled diode string, power is cut off to thehigh-power-consumption device. The first embodiment of the invention mayalternatively include a battery charge sense circuit which produces adigital signal, the digital signal corresponding to either a batterycharge state that is above the predetermined voltage level or a batterycharge state that is below the predetermined voltage level. In onestate, the produced digital signal maintains operability of thehigh-power-consumption device. In the other state, the digital signaldisables the high-power-consumption device. For a preferred firstembodiment apparatus, the invention may also include a visible oraudible warning device that notifies the user of a low battery chargecondition, as well as an emergency manual override switch with whichpower to the high-power-consumption device may be restored regardless ofthe battery charge state. A second embodiment apparatus includesmultiple communication devices in a single portable package, a firstpower supply dedicated exclusively to one of the communication devicesfor which operation over an extended period is critical, and a secondpower supply dedicated to at least one other communication device withinthe single portable package.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009]FIG. 1 is a prior art control circuit which uses a passed throughclock signal to control one of two or more devices powered by a singledepletable power supply;

[0010]FIG. 2 is a block schematic diagram of a first embodiment portablecombination communication device incorporating the invention;

[0011]FIG. 3 is a block schematic diagram of a second embodimentportable combination communication device incorporating the invention;

[0012]FIG. 4 is an electrical schematic diagram of a first embodiment ofthe power management unit;

[0013]FIG. 5 is an electrical schematic diagram of a second embodimentof the power management unit;

[0014]FIG. 6 is a Schmitt trigger circuit constructed from bipolartransistors and resistors;

[0015]FIG. 7 is an operating circuit for the Maxim 921 comparator, asused in the second embodiment of the power management circuit;

[0016]FIG. 8 is a schematic diagram of a first embodiment of a precisionbandgap voltage reference circuit;

[0017]FIG. 9 is a block schematic diagram of a second embodimentportable combination communication device incorporating the invention;and

[0018]FIG. 10 lists the basic steps of the method for implementing theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in terms of a combinationcommunication system which includes a pager and a cellular telephone ina single portable package. Referring now to the block circuit diagram ofFIG. 2, which depicts a first embodiment apparatus, a portablecombination communication system includes dedicated cellular telephonecircuitry 201, dedicated pager circuitry 202, shared circuitry 203 thatis utilized by both the cellular telephone and pager functions, a singleelectrochemical battery 204, which provides power for system operation,and a power management unit 205, which monitors the charge level ofbattery 204 and cuts off the flow of electrical power from the battery204 to the dedicated cellular telephone circuitry 201 when the measuredvoltage drops below a predetermined level that corresponds to a minimumbattery charge level required for continued operation of the dedicatedpager circuitry for a desired period of time. Generally, the desiredperiod of time will be at least 24 hours, which will afford the userample opportunity to return to his/her home or office and eitherrecharge or replace the battery 204. The dedicated pager circuitry 202,the shared circuitry 203 and the power management unit 205 are coupleddirectly to the battery 204 via power bus 206. Power to the dedicatedcellular telephone circuitry is also provided by the battery 204, butvia electrical supply path 207, which is controlled by the powermanagement unit 205. The portable communication system of FIG. 2 alsooptionally includes a low battery charge level warning device 208, whichmay be a visible or audible warning device that notifies the user of alow battery charge condition, as well as an emergency manual overrideswitch 209 by means of which power to the dedicated cellular telephonecircuitry (i.e., the circuitry corresponding to thehigh-power-consumption device) may be restored regardless of the batterycharge state.

[0020] Referring now to FIG. 3, a second embodiment of the combinationcommunication system has no circuitry that is shared by cellulartelephone and pager functions. Consequently, only the dedicated pagercircuitry 202 and the power management unit 205 are powered directly bythe battery 204 via power bus 301. Save for the lack of shared circuitry203, the combination communication system of FIG. 3 is identical in allother respects to the system depicted in FIG. 2.

[0021] Referring now to FIG. 4, an electrical schematic is depicted fora first embodiment of the power management unit 205 of FIGS. 2 and 3.The circuit is a headroom-limited flyback power supply. An oscillator401, powered by battery voltage VBAT, produces a clock signal CLK thatis input to an inverter constructed from field-effect transistors (FETs)QP1 and QN1. When clock signal CLK is low, transistor QP1 will beswitched “on” and transistor QN1 will be switched “off, with node N1being at battery voltage VBAT. A series-coupled diode chain SD1,constructed from diodes D1, D2, D3 and D4, sets the headroom limit bydropping the VBAT value at node N1 by a threshold value through eachdiode. Thus, if each diode has a threshold voltage value of 0.7 volts,node N2 will be about 2.8 volts below VBAT during the clock signal CLK.If V_(T) is the threshold of transistor QN2 (also referred to herein asthe intermediate FET), as long as the high phase of the inverted clocksignal at node N2 is greater than a VT above ground, transistor QN2 willcontinue to switch to the “on” state whenever signal CLK is low and nodeN2 is consequently high. Conversely, when battery voltage VBAT hasdropped to a level such that the high value of the inverted clock signalat node N2 is less than a V_(T) above ground, transistor QN2 will nolonger switch with the clock signal CLK. The resistance value ofresistor R1 is chosen to provide just enough of a current path to groundso that node N2 will discharge sufficiently during the high phase ofsignal CLK to switch transistor QN2 to its “off” state. Resistor R2prevents unnecessary current drain through transistor QN2. The string ofinverters I1, I2 and I3 acts as a buffer to increase the strength of thesignal at node N3. The output of inverter I3 is coupled to the gate oftransistor QN3 (also referred to herein as the final FET). By increasingthe strength of the signal at node N3, the switching between “on” and“off” states of transistor QN3 is greatly improved. Without rapidswitching, a large portion of the energy intermittently stored inflyback inductor LI would be shunted to ground rather than to the outputat node N4. Transistor QN3 provides intermittent current flow throughflyback inductor L1 as long as sufficient headroom between the highinverted clock signal on node N2 and battery voltage VBAT exists. Theresistance value of resistor R3 determines the voltage of a pulsatingoutput at node N4. This pulsating output at node N4 is rectified bydiode D5 and filtered by capacitor C1 to provide a substantially steadyfinal output voltage VOUT. Resistor R4 represents the load imposed bythe cellular phone circuitry 201 of either FIG. 1 or FIG. 2. An optionalP-channel transistor QP2 disables the flyback function when the finaloutput voltage VOUT exceeds a set value. Signal voltage VOFF, whichrepresents the set value of VOUT, is determined by the resistor valuesof the voltage divider formed by resistors R5 and R6. By bringing thegate of QP2 high when the set value of VOUT is reached and therebycutting off current flow through transistors QP1 and QN1, unnecessarypower loss to ground through resistor R3, inductor L1 and transistor QN3is prevented. This is a particularly significant feature when theflyback voltage produced by intermittent current flow inductor L1 issignificantly higher than the desired voltage at VOUT. Alternatively,the values of resistor R3 and inductor L1 can be adjusted so thatflyback voltage, when dropped across diode D5, is equal to the desiredvoltage at VOUT. Thus, even if transistor QN3 continues to switch on andoff, power loss will be minimal.

[0022] Referring now to FIG. 5, an electrical schematic is depicted forthe power management unit 205 of FIGS. 2 and 3. A sample voltage VS thatis proportional to the battery voltage VB is provided with a voltagedivider 501 constructed from resistors R6 and R7. VS is coupled to thenon-inverting input (i.e., the “+” terminal) of a comparator 502. Aprecision reference voltage VR is coupled to the inverting input (i.e.,the “−” terminal) of comparator 502. The values of resistors R6 and R7are selected so that the sample voltage VS is greater than VR, with thedifference between VS and VR corresponding to the voltage range selectedfor continuous operation of the cellular telephone. That is to say thatwhen VS drops below VR, power to the cellular telephone circuitry mustbe cut in order to retain a desired quantity of reserve battery powerfor continued operation of the pager for a desired period. Thus,whenever VS is greater than VR, the output voltage V03 from comparator502 is high. The high voltage level is provided by VB through currentpath 503 through resistor R8. Whenever VS is less than VR, output V03 ispulled to ground, overriding the high voltage provided by current path503. The output from comparator 502 is coupled to the gate of anN-channel field-effect transistor NQ4. When the output from comparator502 is high, NQ4 conducts, providing power to the cellular telephonecircuitry 201. Conversely, when the output from comparator 502 is low,NQ4 is nonconductive, cutting off power to the cellular telephonecircuitry 201. In order to prevent oscillations about the set turnoffpoint (a condition often termed “thrashing”), hysteresis is provided atthe output via a Schmitt trigger. The Schmitt trigger function can beprovided by positive feedback via an optional feedback path 504, whichincorporates resistor R9, or it can be provided by the circuit of FIG. 6in the absence of feedback path 504.

[0023] Referring now to FIG. 6, the Schmitt trigger function is providedin this circuit by a pair of bipolar transistors, NPN1 and NPN2, and aquartet of resistors, R10, R11, R12, and R13. NPN1 and NPN2 shareemitter resistor R13. For proper operation of this circuit, it isessential that R10, NPN1's collector resistor, have a larger resistancevalue than R11, NPN2's collector resistor. Suggested values for R10,R11, R12, and R13 are 1.5 kΩ, 1.0 kΩ, 100Ω and 10 kΩ, respectively.Given such an arrangement, the threshold to turn on NPN1, which is onediode drop above the emitter voltage, rises when NPN1 is turned off,since the emitter current and voltage is higher when NPN2 is conducting.Hysteresis is thereby produced in the trigger threshold.

[0024] The Maxim 921 integrated circuit (IC) is well adapted for use asa comparator for this comparator application, as it incorporates bothhysteresis and a precision bandgap reference voltage in a single ICpackage. FIG. 7 depicts a circuit employing the Maxim 921 device for thepresent application. It is essentially an elegant implementation of thecircuit of FIG. 5. Resistors R14 and R15 provide the same function asresistors R6 and R7 of FIG. 5. The Maxim 921 IC produces an output V04,which controls FET NQ4. Although the voltage reference symbol at pin 2is that of a Zener diode, the Maxim 921 comparator actually utilizes asilicon bandgap reference. It should be noted that, in certain cases, aZener diode might also be utilized to provide a voltage reference forthe present invention. However, as Zener diodes are generally noisy andhave non-zero temperature coefficients, except when operating in theneighborhood of 6.0 volts, bandgap references are typically preferred asvoltage references.

[0025] In a comparator circuit which does not employ the Maxim 921integrated circuit, it will be necessary to design a precision referencecircuit. A precision voltage reference circuit is particularly desirableif the battery 204 is a nickel-cadmium type which has relatively stablevoltage output over its charge range, then drops rather precipitouslywhen nearing a fully discharged condition. An example of a classicV_(BE) circuit, which provides a precision reference voltage derivedfrom the bandgap voltage of silicon, is depicted in FIG. 8. The circuitis constructed from a trio of NPN bipolar transistors NPN3, NPN4 andNPN5, and a quintet of resistors, R16, R17, R18, R19, and R20. ResistorR20 couples a reference node 801 to battery voltage VB. The circuitoperates by generating a voltage with a positive temperature coefficientthat equals the V_(BE)'s negative coefficient. When the two voltages areadded, the resultant voltage has a zero temperature coefficient.Transistors NPN3 and NPN4; by having dissimilar emitter currentdensities (typically a ratio of 10:1), provide a current mirror.Resistor R17 sets the amount of positive-coefficient voltage that isadded to V_(BE). By choosing the appropriate value of R17, a zerooverall temperature coefficient is achieved. It turns out that a zerotemperature coefficient results when total voltageV_(BE)+(R17)(I_(NPN4)) equals the silicon bandgap voltage (extrapolatedto absolute zero), which is about 1.22 volts. This total voltage valueis used as the precision reference voltage VR.

[0026] If even greater precision is required for the reference voltageVR, other precision bandgap reference circuits are available. Forexample, on page 30 of the IEEE Journal of Solid-State Circuits, Vol.SC-19, No.6, December 1984, FIG. 6, depicts an improved CMOS bandgapreference voltage circuit which overcomes two basic disadvantages ofsimple bandgap reference circuits. This circuit, as well as itsaccompanying description, are incorporated herein by reference. Thefirst disadvantage of the simple bandgap reference circuits is that theamplifier offset voltage adds directly to the difference in base-emittervoltages ΔV_(BE) of the bipolar transistors. Offset voltages of typicalCMOS operational amplifiers range between ±15 mV and, when amplified bythe resistor ratio gain factor (1+R₁/R₂), lead to a large variation inthe reference voltage. This increases the reference voltage trimmingrequirements for a required precision. The second disadvantage of thesimple bandgap reference circuits is that the offset voltage of a CMOSop amp drifts with time and has a temperature coefficient of around 20μV/°C. These variations are amplified and degrade the referencestability and performance.

[0027] The improved CMOS bandgap reference voltage circuit, depicted asFIG. 6 of page 30 of the IEEE Journal, employs an area-ratioed stack ofthree closely-matched bipolar transistors to produce a highly-stablereference voltage which is three times the silicon bandgap voltage. Thisreduces the effect of the offset by a factor of 3. The bandgap voltageis given by the following formula:

V _(BG)=3V _(BE)+(3ΔV _(BE) +V _(OS))·(1+R ₁ /R ₂)

[0028] Transistors M₁-M₆ are matched current sources, each of whichforces a current equal to 3 ΔV_(BE)÷R₁/R₂ into each bipolar transistor.The transistors M₇-M₁₁ drop the necessary voltage required to match thecurrents in M₁-M₆ to within 0.5 percent. The resulting output voltageV_(BG) is 3.8 volts.

[0029] Referring now to the block circuit diagram of FIG. 9, depicted isa third embodiment portable communication system. This system includesdedicated cellular telephone circuitry 201, dedicated pager circuitry202, a first DC power source 901 which powers the dedicated cellulartelephone circuitry 201, and a second DC power source 902 which powersthe dedicated pager circuitry 202. As the power requirements of thededicated pager circuitry are minimal, a single alkaline cell can powera pager for up to several weeks. Of course, the second DC power source902 may be either rechargeable or discardable after the charge thereinis exhausted. The first DC power source 901 is preferably rechargeablebecause of the high power consumption requirements of the powered device(i.e., the cellular telephone in this particular example of acombination portable communication device). No power management unit,such as the one employed for the systems of FIGS. 2 and 3 is required,as the pager DC power source 902 is independent from that of thecellular telephone DC power source 901.

[0030] Referring now to FIG. 10, the basic steps are listed for theinvention characterized as a method. For ensuring that, in an electronicdevice having at least two communication devices packaged as a singleunit, sufficient power is provided for extended operation of thecommunication device having the lowest continuous power consumptionrequirements, are the following steps:

[0031] providing a communication system incorporating at least first andsecond communication devices in a single package, the first devicehaving a higher continuous power consumption rate than the seconddevice;

[0032] providing an exhaustible supply of direct-current power withinthe package for the system, said exhaustible supply having a finiteamount of available power;

[0033] dedicating a selected portion of the direct-current power withinthe package to the second device so that it may remain serviceable for adesired period, in spite of the higher power consumption requirements ofthe first communication device.

[0034] A first embodiment of the method employs a separate DC powersource for the second communication device, as heretofore described. Asecond embodiment of the method employs a single DC power source incombination with a power management unit, also as heretofore described.

[0035] It should be evident that the heretofore described apparatusesand method are capable of providing a portable communication systemincorporating at least first and second communication devices, with thefirst device having a higher continuous power consumption rate than thesecond device, wherein functionality of the second communication deviceis maintained for at least a selected period of time, in spite of thehigher continuous power consumption rate of the first communicationdevice.

[0036] Although only several embodiments of the portable combinationcommunication and the corresponding method are described, it will beobvious to those having ordinary skill in the art that changes andmodifications may be made thereto without departing from the scope andthe spirit of the process and products manufactured using the process ashereinafter claimed.

What is claimed is:
 1. A communication package comprising: a firstbattery-powered communication device and a second battery-poweredcommunication device, said first battery-powered communication devicehaving power consumption requirements which are at least an order ofmagnitude greater than those of the second battery-powered communicationdevice; a battery power source for supplying a flow of electricity forpowering both of said first battery-powered communication device andsaid second battery-powered communication device, said a battery powersource having first and second output terminals, said first outputterminal having a potential that is positive with respect to thepotential of said second output terminal, said battery power sourceincluding a first battery and a second battery, said at least onebattery including a first battery and a second battery; and a powermanagement unit for providing an uninterrupted flow of said flow ofelectricity to said second battery-powered communication device for apredetermined period although said at least one battery has insufficientcapacity for providing an uninterrupted flow of said flow of electricityto said first communication device for said predetermined period, saidpower management unit comprising: an oscillator having a clock signal;an inverter including a P-channel FET having a gate coupled to saidclock signal and a channel coupling said first output terminal to anoutput node, and an N-channel FET having a gate coupled to said clocksignal and a channel coupling said second output terminal to said outputnode; a current-limiting resistor; an intermediate FET having a gate anda channel connected in series with said current-limiting resistorcoupling said first output terminal to said second output terminal; aplurality of series-coupled diodes coupling said output node to the gateof said intermediate FET; and a flyback inductor for current from astorage device to intermittently flow through, said intermittent flowbeing controlled by said intermediate FET to provide a pulsating flybackvoltage after rectification and filtering thereof gives an outputvoltage for powering said first battery-powered communication device. 2.The communication package of claim 1, wherein said battery power sourceincludes a first battery and a second battery comprises a first batteryand second battery which together constitute said supply of electricity,said first battery providing said power to said first battery-poweredcommunication device, and said second battery providing said power tosaid second battery-powered communication device.
 3. The communicationpackage of claim 2, wherein said second battery comprises anelectrochemical cell and said first battery comprises a plurality ofelectrochemical cells.
 4. The communication package of claim 1, whereinsaid power management unit includes: a reference voltage; a measuredvoltage representative of a charge level of said battery power source;and a switch for cutting the flow of electricity from said storagedevice to said first battery-powered communication device when themeasured voltage drops below a predetermined level that corresponds to aminimum battery charge level required for continued operation of thesecond battery-powered communication device for a desired period oftime.
 5. The communication package of claim 4, wherein a silicon bandgapcircuit produces said reference voltage.
 6. The communication package ofclaim 4, wherein a voltage divider circuit produces said measuredvoltage.
 7. The communication package of claim 4, which furthercomprises a comparator including: an output; a first input coupled tosaid reference voltage; and a second input coupled to said measuredvoltage.
 8. The communication package of claim 7, wherein said switch isa transistor controlled by said comparator output.
 9. The communicationpackage of claim 4, wherein said second battery-powered communicationdevice is a pager, and said first battery-powered communication deviceis a wireless telephone.
 10. The communication package of claim 1, whichfurther comprises: an intermediate node interposed between saidcurrent-limiting resistor and said intermediate FET; a final FET havinga gate coupled to said intermediate node through at least one buffer,said final FET and said flyback inductor providing a serial current pathbetween said first and said second output terminals; and a final nodewithin the serial current path interposed between said flyback inductorand said final FET, said intermittent flow of said power output takenfrom said final node within the serial current path.
 11. Thecommunication package of claim 10, wherein said intermediate FET andsaid final FET are both N-channel devices.
 12. The communication packageof claim 11, further comprising: an adjustment resistor interposed inthe serial current path having a resistance value setting the outputvoltage.
 13. The communication package of claim 1, further comprising: aflyback shut-off transistor controlled by said output voltage fordisabling said inverter when said output voltage reaches a preset level.14. The communication package of claim 13, further comprising: a voltagedivider which adjusts said preset level.
 15. A plurality ofcommunication devices in a portable package having a single batterypower source for powering said plurality of communication devices andhaving a power management unit, said single battery power sourceincluding a first battery and a second battery, said management unitcomprising: an oscillator producing a clock signal, said oscillatorpowered by one of said first battery and said second battery; aninverter including a P-channel FET having a gate coupled to said clocksignal and a channel coupling a first output terminal to an output node,and an N-channel FET having a gate coupled to said clock signal and achannel coupling a second output terminal to said output node; acurrent-limiting resistor for limiting current supplied by one of saidfirst battery and said second battery; an intermediate FET having a gateand a channel in series with said current-limiting resistor couplingsaid first output terminal to said second output terminal; a pluralityof series-coupled diodes coupling said output node to the gate of saidintermediate FET; a flyback inductor through which current from astorage device intermittently flows, being controlled by saidintermediate FET for providing intermittent output power subsequent torectification and filtering, powers a first of said at least twocommunication devices; an intermediate node interposed between saidcurrent-limiting resistor and said intermediate FET; a final FET havinga gate coupled to said intermediate node through at least one buffer,said final FET and said flyback inductor providing a serial current pathbetween said first and said second output terminals; an adjustmentresistor interposed in the serial current path; and a final node withinthe serial current path, said final node interposed between said flybackinductor and said final FET for said intermittent output power beingtaken from the final node.
 16. The plurality of communication devices ofclaim 15, wherein said intermediate FET and said final FET are bothN-channel devices.
 17. The plurality of communication devices of claim15, wherein said power management unit further comprises: an adjustmentresistor interposed in the serial current path having a resistance valuesetting an output voltage.
 18. A wireless communication device and apager device packaged in a portable package having a single batterypower source for providing power for operating both of saidcommunication devices and having a power management unit, said batterypower source including a first battery and a second battery, said unitcomprising: an oscillator producing a clock signal, said oscillatorpowered by one of said first battery and said second battery; aninverter having both a P-channel FET having a gate coupled to said clocksignal and a channel coupling a first output terminal to an output nodeand an N-channel FET having a gate coupled to said clock signal and achannel coupling a second output terminal to said output node; acurrent-limiting resistor; an intermediate N-channel FET having a gateand a channel connected in series with said current-limiting resistorcoupling said first output terminal to said second output terminal; aplurality of series-coupled diodes coupling said output node to the gateof said intermediate N-channel FET; and a flyback inductor through whichcurrent from a storage device intermittently flows being controlled bysaid intermediate N-channel FET to provide intermittent output powersubsequent to rectification and filtering thereof, powers said wirelesscommunication device.
 19. The wireless communication device and a pagerdevice packaged in a portable package of claim 18, wherein said powermanagement unit further comprises: an intermediate node interposedbetween said current-limiting resistor and said intermediate N-channelFET; and a final FET having a gate coupled to said intermediate nodethrough at least one buffer, said final FET and said flyback inductorproviding a serial current path between said first and said secondoutput terminals, said intermittent output power being taken from afinal node within the serial current path, said final node interposedbetween said flyback inductor and said final FET.
 20. The wirelesscommunication device and a pager device packaged in a portable packageof claim 19, wherein said final FET comprises an N-channel device.